because the vorza cup uses an 8mm bearing which is thicker and stronger than the 10mm bearing which always fails. This setup will allow you to use the same bearings thru out the entire truck. I have over 15 packs thru my XL Flux with zero wear to my bearings. I recently opened the diff up and added more oil then dropped it back in. Keep in mind I run 6s and beat the crap out of my trucks. This mod has been battle tested and works.